Every 6 years the Galilean satellites of Jupiter undergo a long series of mutual eclipses and occultations (partial, annular and total), thanks to the alignment of their orbital plane as viewed from Earth. These are known as PHEMUs (mutual phenomena).
Satellites of other gas giants can also encounter PHEMUs, although the Jovian ones are the most well-known.
The worldwide observing campaign is administered by the Institut de Mecanique Celeste et de Calcul des Ephemerides (IMCCE, Paris). By combining data from numerous observations the ephemerides of the Galilean satellites can be refined.
I won’t post all my results on the Forum – this was just a nice example.